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The photodegradation of Congo red dye by (Y2O3)n ZnO photocomposites was investigated through a sequence of experiments. X-ray diffraction analysis indicates nanocomposites' evolution having the ZnO wurtzite structure with increase in crystallite size and Y2O3 phase segregation, as confirmed by the appearance and gradual growth of the Y2O3 peak. Field emission scanning electron microscopy observations reveal irregular spherical morphology with increased agglomeration due to Y2O3 loading. Diffuse reflectance spectra exhibit bandgap widening and red shift of the absorption edge with the doping process. Brunauer–Emmett–Teller analysis denotes improved porosity as manifested by the surface area, pore diameter, and pore volume increments after yttrium loading. Fortuitously, photocatalysts demonstrate excellent photodegradation rates for CR dye, reaching 93% at a higher rate of 43 × 10–3 min−1. The photocomposite 1% Y2O3–ZnO exhibits a threefold enhancement in the visible photocatalytic process in an aqueous solution. The photocatalytic performance is discussed in detail concerning pH and oxygen species, which contribute to the photodegradation of CR dye. The results obtained in this study clearly highlight the superior performance (Y2O3)n ZnO as a highly efficient photocatalyst in the degradation of dyes in water.

In this work, a sol–gel method has been employed to fabricate Cr-doped ZnO nanoparticles (NPs) in the presence of starch at different annealing temperatures. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and Fourier transforms infrared spectroscopy (FTIR). All samples were defined as hexagonal wurtzite ZnO with particle sizes equal to 26, 22, and 31 nm for pure ZnO, Cr-doped ZnO at 500 °C and 700 °C, respectively. The Cr-doped ZnO photocatalyst at 500 °C shifted the band gap energy of ZnO from 3.16 to 3.09 eV. The nanomaterials' photocatalytic activity was tested through the photodegradation of congo red (CR) under visible light illumination. The results demonstrated that the Cr-doped ZnO annealed at 500 °C is an excellent photocatalyst with enhanced degradation competence towards CR dye by virtue of its reduced size and lower band gap energy. The kinetics of the photodegradation fitted the pseudo-first-order model while the mechanistic investigations revealed the great impact of h+ and ·OH on the degradation process. The starch-stabilized chromium-doped ZnO shows a high photocatalytic activity towards CR, indicating their possible environmental remediation application.

MgO@TiO2@g-C3N4 heteronanostructure was synthesized using a simple ultrasonication technique and assessed potentially to remove Cd (II) from aqueous environments. X-ray diffraction analysis confirms composite formation with mean crystallite size in the range of 4-17 nm while transmission electron microscopy analysis reveals nanosheet-like nanoparticles with the homogeneous elemental distribution. N2 adsorption-desorption measurements indicate the formation of a mesoporous structure with a BET surface area of about 107 m2/g. Fourier-transformed infrared elucidates the presence of O–H, amino groups, triazine, Mg–O, and Ti–O vibrations modes. At the same time, X-ray photoelectron spectroscopy analysis manifests the presence of Mg, O, N, Ti, and C elements. For aqueous Cd (II) ions, the MgO@TiO2@g-C3N4 nanostructure displays a superior adsorption efficiency, reaching 99.94% Cd (II) elimination with an optimum adsorption capacity of 515.86 mg/g in a short duration of 16 min. This study demonstrates the capability of using the MgO@TiO2@g-C3N4 nanostructure as an efficient and reusable adsorbent for the uptake of Cd (II) ions in wastewater treatment and potentially for the removal of other heavy metal ions.